Pressure responsive rheostat



Dec. 31, 1940. l. E. MATHER 2,225,629

PRESSURE RESPONSIVE RHEOSTAT Filed Feb. 10, 1936 2 Sheets-Sheet l Dec.31, 1940. 1. E. MATHER PRESSURE RESPONSIVE RHEOSTAT 2 Sheets-Sheet 2Filed Feb. 10, 1936 12,502 fir-win E .Jfzffier Patented Dec. 31, 1940UNITED STATES PATENT OFFICE Warner Corporation, tion of Virginia.

Chicago, 111., a corpora- Application February 10, 1936, Serial No.63,171

11 Claims.

My invention pertains to pressure and temperature responsive rheostatsand is particularly concerned with rheostats for regulating electricalindicators of the types commonly used on automobiles and for many otherpurposes.

An object of my invention is to provide an improved rheostat which issimple and durable and which will be economical to manufacture.

Another object is to provide an improved rheostat which will moreaccurately respond to the pressure or temperature which it is sought toindicate.

Another object is to provide an improved rheostat which can readily bemanufactured to provide any desired current variation.

Another object is to provide an improved rheostat which can readily beadjusted either to modify its own characteristics in accordance with astandard of comparison or to modify its own characteristics tocompensate for the irregular characteristics of the indicating meanswith which it is used.

Other objects and advantages will become apparent as the descriptionproceeds.

In the drawings,

Figure l is a horizontal section taken on the line ll of Figure 2 andshows a preferred form of my invention;

Figure 2 is a vertical section taken on the line 2-2 of Figure 1;

Figure 3 is a view similar to Figure 1 but showing a modified form of myinvention, this view being taken on the line 3--3 of Figure 4;

Figure 4 is a vertical section taken on the line 44 of Figure 3; and

Figure 5 is a vertical section also taken on the line 4-4 of Figure 3but showing the modification thereof adapted to respond to temperaturevariations.

Referring to Figures 1 and 2 of the drawings, I have shown a preferredform of my invention comprising a base I0 having portion l2 pro-- videdwith a pipe thread so that it can be inserted into a part H such as abranchof a T connection in a conduit of the oiling system of anautomobile engine. The base I 0 may be made hexagonal to facilitate thethreading of the base into the part I4.

The base I0 is provided with a shoulder l6 supporting a cup I6 having anupper end adapted to be closed by a cover 20. The cup l6 and cover 20provide convenient means for inclosing and protecting the operatingparts against dirt, water and injury.

The base I 0 is provided with a bore 22 affording fluid communicationwith the interior of the Bourdon tube 24 supported on the upper end ofthis base. This tube 24 is curved, as indicated in Figure 1, and a sheetmetal strap 26 is soldered or otherwise attached to the end of the tube24 which is remote from the base 10. As clearly shown in the drawings,the main portion of the tube 24 lies between the cup l8 and an arcuatesupport 28 mounted on a plate 30 carried on a second shoulder 32 of thebase In. The strap 26 is bent into the form of a semicircle so that theend 34 of this strap lies within one end of the arcuate support 28.

This arcuate support 28 carries a resistance element 36, there being aninsulating strip 38 between the resistance element and the support. Asecond insulating strip 40 is located on the inside of the resistanceelement and serves to prevent any of the wires of the resistance elementfrom projecting inwardly beyond any of the other wires. This insulatingstrip 40 has a lower edge which terminates at a distance above the loweredge of the resistance element, as indicated at 42, whereby the loweredge of the resistance element is exposed and may be engaged by acontact element such as the shoe 44.

A pin 46 forms a common pivotal connection for the contact shoe 44,lever 48, and end 34 of the strap 26 attached to the Bourdon tube 24.The lever 48 is pivotally attached by a. screw 50 to the upper end of ahollow post 5| which is riveted to the plate 30. The lever 48 has ashort arm 52 carrying a pin 54 receiving one end of a tension spring 56having its other end connected to a pin 56 attached to the end of thecontact shoe 44 opposite the pin 46.

As the pressure of the fluid admitted to the Bourdon tube 24 increases,this tube tends to unwind and moves the end 34 of strap 26 toward thearcuate support 28 and the resistance element carried thereby. Thelinkage by means of which the contact shoe is attached to the stationaryplate 30 multiplies the movement of the Bourdon tube about sixteentimes, thereby permitting the rheostat to respond accurately to verysmall variations in fluid pressure. As the contact shoe 44 is movedtoward the resistance element 36, the lower end of this contact shoe, asviewed in Figure 1, first contacts with the lower end of the resistanceelement and short-circuits the contacted portion of the resistanceelement, thereby reducing the resistance in the circuit of which theresistance element forms a part. Increases in pressure result in causingmore and more of the contact shoe 44 to engage and short-circuit moreand more of the resistance element until, at the maximum pressure atwhich the gauge is designed to operate, the entire resistance elementmay be short-circuited.

It will be appreciated that my rheostat may be so made as to produce anydesired relationship between decrease in resistance and fluid pressureby simply making the curved contact edge of the contact shoe 44 of suchshape as to give the desired characteristic. Furthermore, for any givenshape of the curved contact edge of the contact shoe 44, the operatingcharacteristics of my improved rheostat may be varied by shifting therelationship between the contact shoe 44 and the resistance element 36.This change in relationship may be accomplished by providing themechanism with any desired adjusting means.

In Figures 1 and 2, such adjusting means takes the form of ears 60 and62 integral with opposite ends of the arcuate support 20 and provided,respectively, with slots 64 and 66 for receiving screws 68 and 10 bymeans of which the arcuate support 28 is adjustably attached to thestationary plate 30.

The particular instruments shown in the drawings of this applicationwere designed primarily for use in connection with the indicatinginstruments of automobiles and were intended to receive current from thebattery of an automobile. In automotive practice, the frame andconnected mechanism of the automobile constitute the ground and only onewire is used to connect the battery to the various instruments. Iaccordingly show a single wire I2 leading from a binding post I4 on thecap 20 to the indicating instrument which is not shown. The binding post14 is insulated from the cap 20, and the inner end of this binding postis connected to one end of the resistance element 36 by an electricalconductor I6. For automotive use, the other end of the resistanceelement 36 may be grounded as, for example, by way of rivet I0 andarcuate support 20. This rivet serves to clamp the resistance elementand its insulating strips to the support 28.

A feature of my invention is the firm support afiorded to the operatingelements. In this connection attention is directed to the fact that theplate 30 is firmly secured to the base I0 and carries the support 28 forthe resistance element and also carries the post 5| on which the lever40 and attendant mechanism is operatively supported.

It should be noted that the shoe 44 establishes a rolling contact withthe resistance element 36 and progressively short-circuits successiveturns of the wire of this resistance element as the pressure in theBourdon tube increases. The contact edge of this shoe 44 may besilver-plated to provide the most efficient electrical connection withthe resistance 36.

Another advantage of this form of my invention lies in the particularmounting for the spring 56. This mounting is such that the length ofthis spring does not vary appreciably for all positions of the shoe 44whereby the force exerted by this spring is uniform, giving a uniformcalibration of the instrument. Furthermore, this spring removes allslack from the operating connections for the shoe 44 and thus eliminatesany lag in operation which might otherwise be present.

While I have shown this preferred form of my invention as adapted onlyfor use as a pressure indicator, it is to be understood that thispreferred form may be used with equal facility to respond to temperaturevariations of a medium whose temperature it is desired to indicate. Inutilizing this preferred form as a temperature indicator, the base I0may be modified to carry a gas filled bulb in the manner hereinafterdescribed in connection with Figure 5.

In Figures 3, 4 and 5 of the drawings, I have shown a modified form ofinstrument which does not use the movement amplifying linkage of Figures1 and 2. Referring particularly to Figures 3 and 4, the base I0a isshown as threaded into one end of a fluid conduit I00 which may beconnected with any source of fluid pressure which it is desired toindicate. The base I0a carries a cup I8a provided with a cover 20a forinclosing and protecting the operating parts of the device.

The bore 22a of the base I0a communicates with one end of a Bourdon tube24a attached to the upper end of the base. The other end of the Bourdontube is soldered or otherwise attached to a sheet metal strap I02carrying one end of a silver-plated spring I04 which constitutes thecontact member for engaging the resistance element I06. In this form ofmy invention the resistance element I06 is mounted on the cup Ila, asuitable insulating strip I08 being interposed therebetween. The otherend of the spring I04 is secured to a rigid conductor I I0.

It is to be understood that the operating characteristics of this formof my invention can be varied by shifting the resistance element I06with respect to the contact spring I04. In order to permit this. theparts are provided with suitable slots for receiving the bolts II2 bymeans of which the parts are adjustably secured to the cup I80.

As in the previous form of my invention, the cover 20a is provided witha binding post 14a adapted to be connected by wire with the indicatingmeans located on the instrument board of the automobile. This bindingpost is connected to one end of the resistance element by conductor 16a.

The structure shown in Figure 5 is identical with that shown in Figures3 and 4 except that in this figure the device is adapted to respond totemperature variations instead of pressure variations. For this purposethe base I0b is provided with a gas filled bulb I20 which is in freecommunication with the interior of the Bourdon tube 24a. This gas filledbulb is shown as extending into the water jacket I22 of an automibileengine.

As the temperature of the water increases, the temperature of the gas inthe metal bulb I20 is correspondingly raised, whereupon the pressure ofthe gas is increased a definite amount corresponding to each increase intemperature of the water in the water jacket. The increased pressure ofthe gas in the bulb I2I is communicated to the Bourdon tube 24a andoperates the device in the manner previously described. Where the deviceis to be used for indicating temperatures, the bore in the base I 017which connects the interior of the bulb I20 with the Bourdon tube 24a ismade small in order that substantially all of the gas confined in thedevice will be raised to the full temperature of the water in the waterjacket I22.

I find it desirable to limit the movement of the free end of the Bourdontube 24a of the modification shown in Figures 3, 4 and 5 of thedrawings. I accomplish this by providing the strap I02 with alaterally-projecting flange H4 having an opening H6 receiving a pin H8.This pin may be riveted or otherwise attached to the bottom of the cup18a.

While I have illustrated and described several forms of my invention, itis to be understood that my invention is not limited to the specificdetails shown or described, but that my invention may assume numerousforms and that the scope of my invention is to be limited solely by thefollowing claims.

I claim:

1. In a rheostat of the class described, the combination of a base, aplate firmly mounted thereon, a support adjustably carried by saidplate, a resistance element mounted on said support, a Bourdon tubehaving a movable end and another end secured to said base, means foradmitting fluid pressure to said tube, a lever pivotally mounted on saidplate, a common pivotal mounting for one end of said contact member,said lever and the movable end of said tube, and a connection betweenthe other end of said contact member and said lever normally urging saidends toward each other and the contact member toward the resistanceelement.

2. In a rheostat of the class described, the

on said base, said base including a threaded nipple and a boreconnecting said nipple with said tube, a cup supported on said base, anarcuate electrical resistance supported on said base, means insulatingall but one terminal of said resistance from said cup, a contact memberconnected to said Bourdon tube and rollingly engaging said resistanceupon expansion of said tube, said contact member having an arcuateresistance engaging face of a radius not less than half that of saidresistance and of a substantial length and being so mounted with respectto said resistance that slight movement of said tube effects movement ofthe contact face over a considerable portion of said resistance, a coverfor said cup, a binding post mounted on said cover, and an electricalconnection between said binding post and one end of said resistance.

3. In a rheostat of the class described, the combination of anelectrical resistance, a Bourdon tube, means for admitting fluidpressure to said tube, a contact member for engaging said resistance, amovement-multiplying connection between said tube and said contactmember, said connection including a pivoted lever, a pivotal connectionbetween said lever and one end of said contact member, and a resilientconnection between said lever and the other end of said contact member,said resilient connection having a spring for eliminating slack fromsaid movement-multiplying connection.

4. In a rheostat of the class described, the combination of anelectrical resistance, a Bourdon tube, fluid pressure me: as foreffecting movement of one end of said tube, a contact member adapted toengage said resistance, a lever, a common pivotal mounting for saidlever, the movable end of said tube and the contact, a fixed pivotalmounting for said lever, and resilient means connecting the lever andcontact tending to maintain the contact in engagement with theresistance.

5. In a rheostat of the class described, the combination of anelectrical resistance, a Bourdon tube, fluid pressure means foreffecting SEARCH movement of one end of said tube, a contact memberadapted to engage said resistance, a substantially L-shaped leverpivotally mounted intermediate its ends and having each end connectedbut relatively movable with respect to an end of said contact, meansconnecting a corresponding end of said contact and lever forsimultaneous movement by said tube whereby said contact member is movedover said resistance, and means permitting independent adjustment of thepositions of each end of said resistance.

6. In a rheostat of the class described, the combination of anelectrical resistance, a support, a pair of slot and pin connectionsbetween said resistance and said support, said pins and slots providingsufficient play to permit substantially universal adjustment of saidresistance, a contact member for engaging said resistance, a Bourdontube, means for admitting fluid pressure to said tube, and amovement-multiplying connection between said tube and contact member,said movement-multiplying connection com prising an L-shaped leverpivotally supported intermediate its ends, a pivoted connection betweenthe one end of said lever and one end of said contact member, and aspring connecting the other end of said lever with the other end of saidcontact member.

7. In a rheostat of the class described, the combination of a base, aplate firmly mounted thereon, a support adjustably carried by saidplate, a resistance element mounted on said support, a contact memberadapted to engage said resistance, a Bourdon tube having a movable endand another end secured to said base, means for admitting fluid pressureto said tube, a lever pivotally mounted on said plate, a common pivotalmounting for one end of said contact member, said lever and the movableend of said tube, and a connection between the other end of said contactmember and said lever permitting relative movement between them whentheir opposite ends are moved by said tube.

8. In a rheostat of the class described, the combination of a base, aplate firmly mounted thereon, a support adjustably carried by saidplate, a resistance element mounted on said support, a Bourdon tubehaving a movable end and another end secured to said base, means foradmitting fluid pressure to said tube, a lever pivotally mounted on saidplate, a common pivotal mounting for one end of said contact member,said lever and the movable end of said tube, a. spring connecting theother end of said contact member and said lever, and a housing mountedon said base and enclosing said plate, resistance, tube, and lever.

9. In a rheostat of the class described, the combination of a basecomprising a threaded nipple having a passageway therethrough, a Bourdontube in communication with said passageway and supported on said base, aplate firmly mounted upon said base, a support mounted upon said plate,a resistance element mounted on said support, a contact in co-operativerelationship to said resistance element and actuated by said tube, meanselectrically connecting one end of said element to said base, a cupsupported on said base, a cover for said cup co-operatively associatedtherewith to enclose said tube, plate, and resistance element, a bindingpost mounted upon and insulated from said cover, and an electricalconnection from said post to the other end of said resistance element.

10. In a rheostat of the class described, the

combination of an electrical resistance, a Bourdon tube, fluid pressuremeans for effecting movement of one end of said tube, a contact memberhaving an elongated contact face only a portion of which is adapted toengage said resistance at any time, a common pivotal connection for oneend of said tube and said contact whereby said tube may move one end ofthe contact relative to said resistance, and means defining a floatingpivotal mounting for said contact whereby different portions of the faceof the contact are brought into engagement with said resistance uponmovement thereof by said tube.

11. In a rheostat of the class described, the combination of anelongated electrical resistance having an arcuate shape, a Bourdon tube,fluid pressure means for eifecting movement of one end of said tube, anelongated contact member having an arcuate resistance engaging face of aradius less than the radius of the arcuate resistance, a substantiallyL-shaped lever mounted intermediate its ends for pivotal movement abouta fixed point, said point lying between the arcuate resistance, thearcuate contact face, and the centers of the radii of the arcs, a commonfloating pivotal mounting for the movable end of said tube andcorresponding ends of said contact and lever whereby movement of thetube eflects movement of said ends of the contact and lever with respectto said resistance, and a resilient connection between the other ends ofsaid contact and lever providing a floating pivotal mounting for saidother end of the contact.

IRWIN E. MATHER-

